Corrosion Behavior Of API X60 Pipeline Steels In Sea Mud

Corrosion and protection of pipeline steels buried in sea mud takes more and more attention in marine corrosion science with the exploitation and pipe transportation of ocean petroleum. Because of the particularity of the medium and material, our knowledge of corrosivity of sea mud and behavior of pipeline steel exposed in it is not enough. Thus, in the present paper, weight-loss experiments and electrochemical measurements were performed in simulated sea mud cells to help solve this problem.One-year's weight-loss experiment at room temperature was performed with ERW (electric resistance welding) and SML (Seamless) pipeline steel of API 5L X60 grade in sea mud gathered from Yangtse River estuary of the East China Sea with different types. Besides that, weight-loss contrasting experiment of these pipeline steels at 30, 40, and 50℃ last out for half a year. The results showed that SML exhibits better corrosion resistance to sea mud than ERW. Pipeline steels endure less corrosion in sea mud than other region. Different sea mud results in different corrosion rate. E.g. the rate in deep ooze is 3-4 times of that in sand mud. The rate in sterilized mud is greater than un- sterilized one. The rate picks up with temperature hoist.Corrosion behavior was investigated by these following techniques, linear polarization resistance (LPR), potentio-dynamic polarization and electrochemical impedance measurements (EIS) are involved. By polarization curve and EIS, equivalent circuit in initial corrosion stage was brought forward. With which the oxygen diffusion (oxygen as a depolarizing agent in cathode) mechanism was proposed and discussed. The oxygen diffusion in the cathode zone determines the corrosion behavior of pipeline steel in sea mud.Ash-relevancy between sea mud gene and pipeline steel corrosion parameter is calculated. By which, medium factors' influence is valued, corrosion affecting factor and characteristic of SML and ERW are pointed out, feasibility of electro-chemical parameters estimating pipeline steel's corrosion is analyzed.